The fluid catalytic cracking (FCC) process is responsible for a third of the propylene produced in the world today. The advent of petrochemical FCC processes contributed to significantly increasing the production of both propylene and ethylene. Such processes classically use Y and MFI zeolite-based catalysts, varying the concentration of these according to the load and the characteristics of the process used.
The FCC processes currently used that focus on the production of light olefins exhibit a production limit of about 20% w/w of ethylene and 24% w/w of propylene, and also produce a significant amount of aromatics (about 18% w/w). Thus, a new catalyst system aimed at greater production of light olefins, while simultaneously minimizing the formation of aromatic compounds, is highly desirable.
More recently, there have been publications proposing the use of FER-based additives to increase the production of light olefins (ethylene and propylene) in FCC units. For example, U.S. Pat. No. 6,867,341 discloses a process for fluid catalytic cracking of a naphtha feedstock operating at temperatures from 650° C. to 670° C. The process uses a high Si/Al ratio zeolite FER-based additive. Examples in the mentioned document demonstrate that FER zeolite possesses high selectivity to ethylene and propylene in comparison with the other zeolites examined, such as beta, omega, mordenite, EU-1, SUZ-4, ZSM-22 and ZSM-23.
Along the same lines, we have document WO 2006/098712, which discloses a naphtha fluid catalytic cracking process operating at temperatures from 600° C. to 675° C., using pure FER as an additive. The use of FER as an additive promotes high selectivity to ethylene and propylene with low formation of aromatics. That document compared the use of FER as an additive in FCC processes with the use of other zeolites as additives, including beta, omega, mordenite, EU-1, ZSM-22, ZSM-23, SUZ-4 and MFI zeolites.
Although the FER zeolite exhibits high selectivity to ethylene and propylene with reduced production of aromatics, it exhibits lower catalytic activity than do the zeolites usually employed for maximizing light olefins, such as MFI-type zeolites, due to the fact that its pore openings consist of rings of eight and ten members, which is significantly less when compared to those of the MFI zeolites.
U.S. Document 2010/0105974 discloses a fluid catalytic cracking process of a naphtha feedstock operating at reaction temperatures above 650° C. The document discloses the use of a mixture of catalysts as an additive to the base catalyst in an FCC process. This mixture comprises a first catalyst based on a zeolite with small pores having a pore opening of 3 to 5 Å, which can be Rho, chabazite, ZK-5, ITQ-3, ZK-4, erionite, ferrierite, chinoptilolite, ZSM-22 and mixtures thereof, and a second catalyst based on an intermediate pore zeolite with a pore opening of 5 to 5.5 Å, this zeolite being MFI-type and designated by the authors as nano-silicalite. The zeolite should have a silica-alumina ratio greater than 200.
The use of a catalyst system using the mixture of FER zeolites and nano-silicalite as an additive, however, does not produce a higher yield of light olefins when compared with the use of pure nano-silicalite. Accordingly, the document discloses the use of the mixture for the sole purpose of changing the ethylene/propylene ratio, thus maximizing the production of ethylene, to the detriment of propylene production.
Therefore, the technique still requires additives for use in FCC processes that maximize production of light olefins, particularly ethylene and propylene, and that exhibit high activity, as described in detail below.